def extract_ref_seq_name(sam_file):
  """
  Extracts the reference sequence name from the SAM alignment file.

  Args:
    sam_file: Path to the SAM alignment file.

  Yields:
    The reference sequence name for each @SQ header line.
  """

  with open(sam_file, 'r') as f:
    for line in f:
      if line.startswith('@SQ'):
        fields = line.strip().split('\t')
        ref_seq_name = fields[1].split(':')[1] 
        yield ref_seq_name

# Example usage:
sam_file_path = "1_1_S1.sam" 

for ref_seq_name in extract_ref_seq_name(sam_file_path):
  print("grep ", ref_seq_name, " mitochondrion.1.1.genomic.fna")